This invention relates to grain fractionation and more particularly to fractionation of an oat groat by isolating the coarse branny part of a ground oat groat and extracting oat gum, oat protein, and other by-products from the coarse fraction.
Fractionation of any grain-- and especially the oat grain-- is beneficial because each fraction of the grain is usually more valuable than the whole grain itself. The oat seed from which the oat grain is taken comprises an oat hull and an oat groat. The oat hull serves as an outer covering of the groat. The oat groat is comprised of oat bran, including the pericarp and the aleurone layers, germ and endosperm. It is desirable to fractionate the oat groat to obtain oat gum, oat protein, and by-products.
It is well known in the art how to clean, dry, and dehull whole oats. It is further well known to dry the resulting dehulled oat groats under controlled conditions relating to temperature and time. These conditions permit the inactivation of lipolytic enzyme activity which is concentrated in the bran layers of the oat. Such an inactivation retards the subsequent development of rancidity of the oat oil after the groat is ruptured during processing. The controlled conditions of time and temperature during drying are selected to minimize gelatinization of the starch present in the endosperm and other functional changes in the groat.
It is also known to grind the oat groat to separate the bran layers from the starchy portion of the endosperm. This grinding results in a flour comprising two general types of particles. A first type of particle is a small regular shaped spherical particle which basically originates from the starch endosperm. A second type of particle is a more irregularly shaped particle which largely originates from the bran layer or from the endosperm near the bran layer. Particles containing the bran particles or multiple starch granules cemented together by oat gum or protein tend to be less dense and/or more irregularly shaped than the free starch particles from the starch endosperm which tend to be dense and compact. These particles are generally spherical in shape but not necessarily a perfect sphere. These physical distinctions between the particles of the flour formed by grinding the oat groats lend themselves to air classication and separation. Air classification separates the flour by suspending the particles in air and separates on the basis of density, size, and shape. The dense compact particles separate as fines, and the irregular particles separate as a light, coarse flour from air classification.
A major portion of both the oat protein and the oat gum separate on air classification with the coarse oat flour. It is possible to concentrate an even greater portion of oat gum and oat protein in the coarse oat flour if the air classification step and size reduction steps are preceded by extraction of a major part of the lipid faction from the oat groat. The oat groat is rolled to form flakes. The lipid faction is extracted from the flaked oat groat by use of techniques and solvents well known in the art of oil-seed extraction. Specifically, the use of normal hexane extraction in a standard oil-seed extraction process reduces the residual oat lipid in the groat to less than 1 percent. The lipid faction thus removed from the oat groat is generically known as crude oat oil. The crude oat oil usually comprises about 6 percent to about 10 percent by weight of the groat. Removal of this crude oat oil from the groat provides the better classification of the oat protein and the oat gum with the coarse fraction.
Thus it can be seen that oat gum and oat protein can be concentrated into the coarse oat flour by procedures known in the art. Further treatment of the coarse oat flour to isolate gum, protein, and starch is difficult. Enzymes naturally present in the oat groat for the purpose of hydrolyzing the oat gum during the natural process of germination interfere with the separation of the gum. The controlled heating and drying treatment to inactivate lipolytic enzymes in the oat groat leaves a residual glucosidase activity. This enzyme thus remains to interfere with the recovery of the oat gum.
For example, if the coarse oat flour is hydrated to extract the oat gum as is commonly done with other oil-seeds to extract proteins, the native enzymes immediately hydrolyze the oat gum so that it can be neither recovered nor useful. If the coarse flour is hydrated in hot water to inactivate the enzyme, the oat starch present in the coarse oat flour is gelatinized, and thus becomes inseparable from the hydrated gum. So either the enzyme or the starch interferes with the hydrated gum.
Furthermore, the separation of the proteins from the coarse portion is rendered difficult. Not only must gelatinization of the starch be avoided, but hydrolysis of the oat gum must also be avoided. These reactions are opposite reactions. If one reaction is favored, the other reaction takes place to interfere with the fractionation. Oat gum is a water soluble carbohydrate. It is a high molecular weight polymer of glucose with alternating cycles of 2 beta-1,4 linkages followed by two to four alpha-1,4 linkages. Oat gum differs from other polymers of glucose by those specific linkages present between the glucose molecules. For example, in starch, alpha-1,4 linkages with branched chains on the polymer connected with alpha-1,6 linkages are present. In cellulose, the glucose monomer is polymerized with beta-1,4 linkages. This combination of linkages in the oat gum renders the oat seed specifically susceptible to the enzymes present in the hull and groat during germination of the oat seed. The gum is rapidly hydrolyzed to glucose as it becomes hydrated. The resulting glucose provides the energy for the germinating process. Thus it can be concluded that many conventional techniques for separation of cereal components cannot be successfully applied to separate pure oat gum in an intact polymeric form.
Oat protein exists in the oat groat at about 14 to about 22 percent on a dry basis by weight. It is well known that oat protein has a higher nutritional value than other cereal proteins because of the larger and more balanced concentration of the amino acids. Amino acids are essential to human life because they are the basic materials for forming the required protein. If the oat protein is isolatable, one has a suitable material for adding protein content to a variety of foods or forming a desirable protein component.
Thus it may be seen that the physical and bio-chemical composition of the oat grain renders it difficult to separate oat gum, oat protein, and by-products in relatively pure form. It, therefore, becomes obvious that fractionation of the oat seed is a difficult and complex problem having many interfering factors which prevent the effective fractionation of the groats.